1. Field of the Invention
The present invention relates to an image sensor and an image capture apparatus using the same.
2. Description of the Related Art
As image capture apparatuses such as a digital camera and a digital video camera, image capture apparatuses capable of acquiring a still image and a moving image using image sensors such as a CMOS image sensor are prevailing. Such an image capture apparatus is required to improve the continuous shooting speed of a still image or the frame rate of a moving image, thus making it necessary to speed up signal readout from the image sensor. This image capture apparatus is also required to have a large number of pixels so as to achieve high image quality. Hence, to process a large number of pixel signals within a predetermined period of time, it is again necessary to speed up signal readout from the image sensor.
To meet such a requirement of speedup of signal readout, a multi-channel image sensor including a plurality of readout channels formed by horizontal output circuits and readout amplifiers has come to be generally used. An image capture apparatus which employs a multi-channel image sensor is generally configured to convert pixel signals output from the image sensor into digital data using an A/D converter arranged for each channel, and then rearrange the pixel signals to generate a single image.
However, the offset characteristics, gain characteristics, and linearity characteristics of, for example, the horizontal output circuit, readout amplifier, and A/D converter (analog-to-digital converter) on each channel may vary in each individual channel.
Assume, for example, that signals from an image sensor formed by arraying pixels in an RGB Bayer arrangement are read via a plurality of channels. In this case, when signals of the same color are read to different channels while the individual channels have the above-mentioned variations in characteristics, fixed pattern noise such as vertical streaks/horizontal streaks may be produced in the image. To reduce such fixed pattern noise, a configuration which outputs signals of the same color to the same channel has been proposed.
Japanese Patent Laid-Open No. 2007-174478, for example, proposes the following configuration. That is, signals are output from pixels on odd columns to one of two horizontal output circuits in readout from odd rows, and signals are output from pixels on even columns to this horizontal output circuit in readout from even rows. In contrast to this, signals are output from pixels on even columns to the other horizontal output circuit in readout from odd rows, and signals are output from pixels on odd columns in readout from even rows. Upon this operation, signals of the same color are output to the same channel in the image sensor having the Bayer arrangement, thus reducing fixed pattern noise.
However, to perform readout processing at a higher speed, it is also possible to provide three or more horizontal output circuits and perform multi-channel readout using three or more channels. In this case as well, the above-mentioned configuration in Japanese Patent Laid-Open No. 2007-174478 reads signals of the same color via pluralities of horizontal output circuits, readout amplifiers, and A/D converters. Accordingly, variations in characteristics in each individual channel appear in an output image as fixed pattern noise.